The invention relates to forging of workpieces, particularly metal workpieces such as reinforcing bars for use in building construction, particularly concrete construction.
Concrete reinforcing bars, which may be deformed by external ribs, or plain, are usually provided in finite lengths.
It is often necessary to join them in line to provide a more extensive reinforcement than might otherwise be possible owing to the finite length. Such bars have a high tensile strength, and it is accordingly necessary not to undermine that strength during any process to enable the bar to be connected with another. Usually this is effected by providing a thread on one end, usually by cold working, which can be advantageous as the bars are usually made from steel with a high carbon and manganese content. However, forming a thread at one end of the bar often reduces the cross-section of the bar, thus lowering its tensile cross-section in the region of the thread, which leads to failure in use, which can be catastrophic for the concrete. It is thus necessary to ensure that the threaded end (which is formed by rolling, milling or cutting) is enlarged, relative to the remaining length of the bar, so that the effective tension cross-section of the threaded part is not smaller than that of the remaining length of bar. However, in the past, enlarging techniques have not been able satisfactorily to produce an enlarged end of a ribbed bar in which the tensile strength is not effected as compared with that of the remainder of the bar.
It is an object of the invention to seek to mitigate these disadvantages.
According to a first aspect of the invention there is provided apparatus for cold forging a metal workpiece, comprising a die with means to alleviate stress to the workpiece during forging.
According to a second aspect of the invention there is provided apparatus for enlarging part of a metal workpiece by cold forging, comprising an enlarging die with means to alleviate stress to the workpiece during forging.
Using the invention it is possible to provide an enlarged end of deformed (ribbed) and undeformed reinforcement bars without changing their overall tensile characteristics.
The stress alleviating means may comprise a relief channel into which metal can flow during forging. This is a relatively simple yet effective construction, particularly where the relief channel may be a substantially U-shaped groove in the die.
There may be two opposed dies. This provides for positive enlargement over the whole circumference of the workpiece.
Each die may have a first die part and a second die part which second die part may be enlarged relative to the first die part and may be adapted to allow part of the workpiece to project therefrom, the arrangement being such that in use the projecting part of the workpiece is upset and enlarged. This is a particularly simple and efficient construction.
There may be means to press the die parts together, and means to apply pressure in a direction substantially at 90xc2x0 to the first-mentioned press direction. This provides for maintaining a tensile integrity of the workpiece during a forging/enlarging procedure.
The means for pressing the die parts together may comprise an hydraulic press acting substantially vertically in use. This is an effective construction.
The second-mentioned means may comprise an hydraulic press acting substantially horizontally. This is also an effective construction.
At least the distance between the enlarging die and the substantially-horizontally acting hydraulic press may be adjustable. This provides for a desired enlarging operation.
The distance may be adjustable by adjusting the pressure of a forging piston for effecting forging. This is an effective way of adjusting the operation.
An equally effective alternative may be by the distance being adjustable by adjustment of a forging pad on which the forging piston can act.
The pressure of the substantially vertically acting hydraulic press may also be adjustable. This again provides a desired control of the procedure.
The first die part may have an internal die configuration substantially complementary to the external configuration of a major part of a workpiece which is to be forged. This provides for support of the workpiece during enlargement.
According to a third aspect of the invention there is provided a method of cold forging an elongate metal workpiece, comprising the steps of providing forging apparatus having a die, providing the die with means to alleviate stress in the workpiece during forging, and forging the workpiece.
The method may include the steps of providing two opposed forging dies. This provides a positive method of operation.
Each forging die may comprise a relief channel into which material of the workpiece can flow during forging. This provides that the tensile integrity of the workpiece is maintained.
There may be the steps of providing that each die part has a first die part and a second die part enlarged with respect to the first die part, inserting an elongate workpiece between the dies so that the first die part receives a main part of the workpiece, and an end of the workpiece projects through and beyond the second die part, and upsetting the projecting end so that it flows into the enlarged second die part. This provides an efficient method of enlargement.
There may be the steps of removing the forged workpiece from the apparatus and forming a thread on the enlarged part of the workpiece. This provides a way to connect the workpiece with another similar one.
According to a fourth aspect of the invention there is provided an elongate metal workpiece whenever forged by a method as hereinbefore defined, or whenever produced by a method as hereinbefore defined.
The elongate metal workpiece may have at least one threaded end, and may comprise a reinforcing bar for use in building construction.
Such a reinforcing bar may have an internally threaded sleeve on an end opposite an enlarged threaded end.
According to a fifth aspect of the invention there is provided a reinforcing system, comprising a plurality of reinforcing bars as hereinbefore defined.
According to a sixth aspect of the invention there is provided concrete whenever reinforced by a workpiece or reinforcing bar as hereinbefore defined.